Display devices used while being worn on human bodies, such as display devices mounted on heads, have recently been developed and are referred to as head-mounted displays or wearable displays. It is desired that not only display devices but also electronic devices used while being worn on human bodies, such as hearing aids, have a light weight and a small size.
Along with a decrease in weight of electronic devices, it is demanded that batteries for supplying power to electronic devices also have a light weight and a small size.
Electronic books including flexible display devices are disclosed in Patent Documents 1 and 2.